test(daemon): add fake_dragonxd, a slow dragonxd stand-in for stop/kill testing

A scriptable fake dragonxd that reproduces, in minutes, the incident where
the GUI hard-killed a node busy with an hour-long witness rebuild:

- dragonxd's HTTP-RPC queue (8 workers + 16 queued, -rpcthreads /
  -rpcworkqueue honoured): a full queue answers an immediate plain-text
  500 "Work queue depth exceeded", and a request whose client gave up
  keeps its slot until a worker reaches it
- a global cs_main held by a "witness rebuild" that logs the real
  markers; every method except stop/help takes it
- warmup -28 with the daemon's allow-list, an optional startup replay
- dragonxd's shutdown order: stop (or SIGTERM on POSIX) unbinds RPC,
  503s open connections, waits for the rebuild, then logs
  "Shutdown: In progress..." / "Shutdown: done" and exits 0

Everything is appended to <datadir>/fake_dragonxd.events; a missing
"clean-exit" line means the process was killed. One portable C++17 file
(POSIX + Winsock), OFF by default (-DDRAGONX_BUILD_FAKE_DAEMON=ON), built
into <build>/fake_dragonxd/ so it can't shadow the real bin/dragonxd.
run-gui-with-fake.sh runs the GUI against it in a throwaway HOME.

Against master's GUI on Linux it reproduces the bug: closing during a
rebuild queues stop behind cs_main-blocked workers, then the GUI sends
SIGTERM and SIGKILL mid-rebuild, with no clean exit.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

CMakeLists.txt

@@ -45,6 +45,7 @@ option(DRAGONX_ENABLE_EMBEDDED_DAEMON "Enable embedded dragonxd support" ON)
 option(DRAGONX_BUILD_LITE "Build ObsidianDragonLite variant without full-node features" OFF)
 option(DRAGONX_ENABLE_LITE_BACKEND "Enable real lite wallet backend integration" OFF)
 option(DRAGONX_ENABLE_CHAT "Enable the HushChat protocol/UI integration" ON)
+option(DRAGONX_BUILD_FAKE_DAEMON "Build the fake slow dragonxd test stub (tools/fake_dragonxd); never shipped" OFF)
 set(DRAGONX_LITE_BACKEND_LIBRARY "" CACHE FILEPATH "Path to a prebuilt SDXL-compatible lite backend library")
 set(DRAGONX_LITE_BACKEND_INCLUDE_DIR "" CACHE PATH "Optional include directory for SDXL-compatible lite backend headers")
 set(DRAGONX_LITE_BACKEND_EXTRA_LIBS "" CACHE STRING "Additional libraries needed by the SDXL-compatible lite backend")
@@ -1105,6 +1106,27 @@ else()
     message(STATUS "wallet-rebuild helper: OFF (no Berkeley DB found; set DRAGONX_BDB_ROOT for release builds)")
 endif()
 
+# -----------------------------------------------------------------------------
+# fake_dragonxd — a deliberately slow, scriptable dragonxd stand-in that reproduces the daemon-stop
+# incident (usage and the incident it models: tools/fake_dragonxd/README.md).
+# Test tooling only: OFF by default, never packaged, and written to <build>/fake_dragonxd/ so its
+# "dragonxd" name can't shadow the real bin/dragonxd.
+# -----------------------------------------------------------------------------
+if(DRAGONX_BUILD_FAKE_DAEMON)
+    add_executable(fake_dragonxd tools/fake_dragonxd/fake_dragonxd.cpp)
+    target_link_libraries(fake_dragonxd PRIVATE nlohmann_json::nlohmann_json)
+    if(WIN32)
+        target_link_libraries(fake_dragonxd PRIVATE ws2_32)
+    else()
+        find_package(Threads REQUIRED)
+        target_link_libraries(fake_dragonxd PRIVATE Threads::Threads)
+    endif()
+    set_target_properties(fake_dragonxd PROPERTIES
+        OUTPUT_NAME dragonxd
+        RUNTIME_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/fake_dragonxd)
+    message(STATUS "fake_dragonxd test stub: ON (${CMAKE_BINARY_DIR}/fake_dragonxd/)")
+endif()
+
 # -----------------------------------------------------------------------------
 # Tests
 # -----------------------------------------------------------------------------